Nutrient loss pathways from grazed grasslands and the effects of decreasing inputs: experimental results for three soil types

Agriculture is a main contributor of diffuse emissions of N and P to the environment. For N the main loss pathways are NH₃-volatilization, leaching to ground and surface water and N₂(O) emissions. Currently, imposing restraints on farm inputs are used as policy tool to decrease N and P leaching to ground water and to surface water, and the same measure is suggested to combat emissions of N₂O. The response, however, to these measures largely depends on the soil type. In this study nutrient flows of three dairy farms in The Netherlands with comparable intensity on sand, peat and clay soils were monitored for at least 2 years. The first aim was to provide quantitative data on current nutrient loss pathways. The second aim was to explore the responses in partitioning of the nutrient loss pathways when farm inputs were altered. Mean denitrification rates ranged from 103 kg N ha⁻¹ year⁻¹ for the sandy soil to 170 kg N ha⁻¹ year⁻¹ for the peat soil and leaching to surface water was about 73 kg N ha⁻¹ year⁻¹ for the sandy soil, 15 kg N ha⁻¹ year⁻¹ for the clay soil and 38 kg N ha⁻¹ year⁻¹ for the peat soil. For P, leaching to surface water ranged from 2 kg P ha⁻¹ year⁻¹ for the sandy site to 5 kg P ha⁻¹ year⁻¹ for the peat site. The sandy soil was most responsive to changes in N surpluses on leaching to surface water, followed by the peat soil and least responsive was the clay soil. For P, a similar sequence was found. This article demonstrates that similar reductions of N and P inputs result in different responses in N and P loss pathways for different soil types. These differences should be taken into account when evaluating measures to improve environmental performance of (dairy) farms.     

Emissions of N<Subscript>2</Subscript>O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N₂O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N₂O ha⁻¹ year⁻¹ for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N₂O ha⁻¹ year⁻¹. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N₂O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N₂O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N₂O emissions such as groundwater level. In this paper we report on the relations between N₂O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N₂O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N₂O–N ha⁻¹ year⁻¹ and 11.6 kg N–N₂O ha⁻¹ year⁻¹ for the dry and wet conditions, respectively. Especially under dry conditions, measured N₂O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N₂O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level (R ² = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soils.     

Soil carbon stocks under present and future climate with specific reference to European ecoregions

World soils and terrestrial ecosystems have been a source of atmospheric abundance of CO₂ ever since settled agriculture began about 10–13 millennia ago. The amount of CO₂-C emitted into the atmosphere is estimated at 136 ± 55 Pg from terrestrial ecosystems, of which emission from world soils is estimated at 78 ± 12 Pg. Conversion of natural to agricultural ecosystems decreases soil organic carbon (SOC) pool by 30–50% over 50–100 years in temperate regions, and 50–75% over 20–50 years in tropical climates. The projected global warming, with estimated increase in mean annual temperature of 4–6°C by 2100, may have a profound impact on the total soil C pool and its dynamics. The SOC pool may increase due to increase in biomass production and accretion into the soil due to the so-called “CO₂ fertilization effect”, which may also enhance production of the root biomass. Increase in weathering of silicates due to increase in temperature, and that of the formation of secondary carbonates due to increase in partial pressure of CO₂ in soil air may also increase the total C pool. In contrast, however, SOC pool may decrease because of: (i) increase in rate of respiration and mineralization, (ii) increase in losses by soil erosion, and (iii) decrease in protective effects of stable aggregates which encapsulate organic matter. Furthermore, the relative increase in temperature projected to be more in arctic and boreal regions, will render Cryosols under permafrost from a net sink to a net source of CO₂ if and when permafrost thaws. Thus, SOC pool of world soils may decrease with increase in mean global temperature. In contrast, the biotic pool may increase primarily because of the CO₂ fertilization effect. The magnitude of CO₂ fertilization effect may be constrained by lack of essential nutrients (e.g., N, P) and water. The potential of SOC sequestration in agricultural soils of Europe is 70–190 Tg C yr⁻¹. This potential is realizable through adoption of recommended land use and management, and restoration of degraded soils and ecosystems including wetlands.     

Horizontal nutrient flows and balances in irrigated urban gardens of Khartoum, Sudan

The role of urban agriculture (UA) for the supply of fresh vegetables, fruits and meat for local markets is well known. The periodically flooded Gerif soils on the River Nile banks in the core of Khartoum city harbour vegetable gardens that supply perishable leafy vegetables with a short life cycle. In an effort to assess their sustainability and possible negative environmental impact we used a horizontal balance approach to determine the nutrient use efficiency of four intensively cropped UA gardens. Two of the gardens were located in downstream lowlands (L1 and L2) and the other two belonged to the upstream highlands (H1 and H2). The river sediments contributed on average 873 kg nitrogen (N), 6.5 kg phosphorus (P), 6.8 kg potassium (K) and 8,317 kg carbon (C) per hectare in lowland gardens, while only 289, 1.6, 2.5 and 1,938 kg N, P, K and C ha⁻¹ reached the highlands. The farmers’ management in all four gardens resulted in horizontal N and C surpluses of 75–342 kg N ha⁻¹ year⁻¹ and 798–6,412 kg C ha⁻¹ year⁻¹, in contrast to P and K for which negative balances up to −45 kg P ha⁻¹ year⁻¹ and −583 kg K ha⁻¹ year⁻¹ were recorded. While the River Nile floods as important N and C source contribute significantly to soil fertility maintenance, the negative P and K balances call for a better integration of UA gardening with livestock husbandry and the regular addition of animal manure in these cropping systems.     

Carbon sequestration in soils of cool temperate regions (introductory and editorial)

The cool temperate climate, dominance of perennial land use, and relatively large proportion of peat and organically rich soils, make the northern European regions to have a large potential of soil organic carbon (SOC) sequestration. However, with predicted global warming soils in these areas may become sources of atmospheric CO₂. Quantitative and reliable assessment methods and understanding of the spatial variability of SOC pools are required to make accurate mean estimate of available C and integrate variability into predictive models of SOC reserves and sequestration potential. Advanced analytical methods such as near-infrared spectroscopy and carbon isotope techniques can be used to estimate retention time and C turnover rates in soils. The rehabilitation of peat lands has shown a potential for SOC sequestration ranging from 25 to 45 gCm⁻² yr⁻¹ in Scandinavian countries. The potential of SOC sequestration in agricultural and forestry ecosystems depends on the land use and management practice adopted. Furthermore, the proven land management practices (e.g. conservation tillage, reduced soil erosion, restoring wetlands and degraded lands) coupled with improved cultivation practices (e.g. judicious fertilizer use, crop rotations and cover crops) can make the soil of this region as C sink.     

Soil organic carbon changes and distribution in cultivated and restored grassland soils in Saskatchewan

The impacts of grassland restoration on amounts, forms and distribution of soil organic carbon (SOC) were examined in paired cultivated and restored grassland catenae of the Missouri Coteau region in south-central Saskatchewan, Canada. Total SOC (0–15 cm depth) and light fraction organic carbon (LFOC) (0–7.5 cm) contents were determined in paired catenae in upland areas, and in the surface (0–15 cm) and at depth (>15 cm) in the wetland fringe areas. Mass of SOC was higher in the restored grassland catenae than in the cultivated equivalents. In both the cultivated and restored grassland catenae at the three sites, footslope positions consistently had a higher mass of SOC. However, the shoulder positions showed the greatest response in soil C sequestration to grass seed-down, with a 1.4–2.9 Mg ha⁻¹ year⁻¹ SOC increase apparent over an approximately eight-year period. The mass of LFOC and the proportion of SOC comprised of LFOC was also higher in the restored grassland, reflective of higher recent C inputs. Rates of C sequestration in the Missouri Coteau based on SOC differences in the paired comparisons were estimated to be 0.3–2.9 Mg C ha⁻¹ year⁻¹, depending upon site and slope position. In the wetland fringe region of the landscape, the three sites also had higher surface or subsurface SOC in the grassland restoration. In general, SOC changes at depth (below 15 cm) in the restored grasslands appeared to be less consistent than changes in SOC in the surface 0–15 cm soil. In conclusion, the findings suggest that a switch to permanent cover on these soils will significantly increase C sequestered in the soil.     

Soil carbon,soil nitrate,and soil emissions of nitrous oxide during cultivation of energy crops

Carbon (C) sequestration and soil emissions of nitrous oxide (N₂O) affect the carbon dioxide (CO₂) advantage of energy crops. A long-term study has been performed to evaluate the environmental effects of energy crop cultivation on the loamy sand soil of the drier northeast region of Germany. The experimental field, established in 1994, consisted of columns (0.25 ha each) cultivated with short rotation coppice (SRC: Salix and Populus) and columns cultivated with annual crops. The columns were subdivided into four blocks, with each receiving different fertilization treatments. The soil C content was measured annually from 1994 until 1997, and then in 2006. Soil N₂O levels were measured several times per week from 1999 to 2007. Water-filled pore space (WFPS) and soil nitrate measurements have been performed weekly since 2003. Increased C stocks were found in SRC columns, and C loss was observed in blocks with annual crops. The soil from fertilized blocks had higher levels of C than the soil from non-fertilized blocks. SRC cropping systems on dry, loamy sand soils are advantageous relative to annual cropping systems because of higher C sequestration, lower fertilized-induced N₂O emissions, and reduced background N₂O emissions in these soils. SRC cropping systems on dry, loamy sand soils have a CO₂ advantage (approximately 4 Mg CO₂ ha⁻¹ year⁻¹) relative to annual cropping systems.     

Nitrous oxide emissions from fertilized and unfertilized grasslands on peat soil

Emissions of nitrous oxide (N₂O) from managed and grazed grasslands on peat soils are amongst the highest emissions in the world per unit of surface of agriculturally managed soil. According to the IPCC methodology, the direct N₂O emissions from managed organic soils is the sum of N₂O emissions derived from N input, including fertilizers, urine and dung of grazing cattle, and a constant ‘background’ N₂O emission from decomposition of organic matter that depends on agro-climatic zone. In this paper we questioned the constant nature of this background emission from peat soils by monitoring N₂O emissions, groundwater levels, N inputs and soil NO₃ ⁻–N contents from 4 grazed and fertilized grassland fields on managed organic peat soil. Two fields had a relatively low groundwater level (‘dry’ fields) and two fields had a relatively high groundwater level (‘wet’ fields). To measure the background N₂O emission, unfertilized sub-plots were installed in each field. Measurements were performed monthly and after selected management events for 2 years (2008–2009). On the managed fields average cumulative emission equaled 21 ± 2 kg N ha⁻¹y⁻¹ for the ‘dry’ fields and 14 ± 3 kg N ha⁻¹y⁻¹ for the ‘wet’ fields. On the unfertilized sub-plots emissions equaled 4 ± 0.6 kg N ha⁻¹y⁻¹ for the ‘dry’ fields and 1 ± 0.7 kg N ha⁻¹y⁻¹ for the ‘wet’ fields, which is below the currently used estimates. Background emissions were closely correlated with groundwater level (R ² = 0.73) and accounted for approximately 22% of the cumulative N₂O emission for the dry fields and for approximately 10% of the cumulative N₂O emissions from the wet fields. The results of this study demonstrate that the accuracy of estimating direct N₂O emissions from peat soils can be improved by approximately 20% by applying a background emission of N₂O that depends on annual average groundwater level rather than applying a constant value.     

Long-term tillage,straw management and N fertilization effects on quantity and quality of organic C and N in a Black Chernozem soil

Soil, crop and fertilizer management practices may affect the amount and quality of organic C and N in soil. A long-term field experiment (growing barley, wheat, or canola) was conducted on a Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, to determine the influence of 19 (1980 to 1998) or 27 years (1980 to 2006) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [S_Rem]and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha⁻¹ in S_Ret and 0 kg N ha⁻¹ in S_Rem plots) on total organic C (TOC) and N (TON), and light fraction organic C (LFOC) and N (LFON) in the 0–7.5 and 7.5–15 cm or 0–5, 5–10 and 10–15 cm soil layers. The mass of TOC and TON in soil was usually higher in S_Ret than in S_Rem treatment (by 3.44 Mg C ha⁻¹ for TOC and 0.248 Mg N ha⁻¹ for TON after 27 years), but there was little effect of tillage and N fertilization on these parameters. The mass of LFOC and LFON in soil tended to increase with S_Ret (by 285 kg C ha⁻¹ for LFOC and 12.6 kg N ha⁻¹ for LFON with annual rate of 100 kg N ha⁻¹ for 27 years)_, increased with N fertilizer application (by 517 kg C ha⁻¹ for LFOC and 36.0 kg N ha⁻¹ for LFON after 27 years), but was usually higher under CT than ZT (by 451 kg C ha⁻¹ for LFOC and 25.3 kg N ha⁻¹ for LFON after 27 years). Correlations between soil organic C or N fractions were highly significant in most cases. Linear regressions between crop residue C input and soil organic C or N were significant in most cases. The effects of tillage, straw management and N fertilizer on soil were more pronounced for LFOC and LFON than TOC and TON, and also in the surface layers than in the deeper layers. Tillage and straw management had little or no effect on C:N ratios, but the C:N ratios in light organic fractions significantly decreased with increasing N rate (from 20.06 at zero-N to 18.91 at 100 kg N ha⁻¹). Compared to the 1979 results, in treatments that did not receive N fertilizer (CTS_Rem0, CTS_Ret0, ZTS_Rem0 and ZTS_Ret0), CTS_Rem0 resulted in a net decrease in TOC concentration (by 1.9 g C kg⁻¹) in the 0–15 cm soil layer in 2007 (after 27 years), with little or no change in the CTS_Ret0 and ZTS_Rem0 treatments, while there was a net increase in TOC concentration (by 1.2 g C kg⁻¹) in the ZTS_Ret0 treatment. Straw retention and N fertilizer application at 50 and 100 kg N ha⁻¹ rates showed a net positive effect on TOC concentration under both ZT (ZTS_Ret50 by 2.3 g C kg⁻¹ and ZTS_Ret100 by 3.1 g C kg⁻¹) and CT (CTS_Ret50 by 3.5 g C kg⁻¹ and CTS_Ret100 by 1.6 g C kg⁻¹) treatments in 2007 compared to 1979 data. In conclusion, the findings suggest that retention of straw, application of N fertilizer and elimination of tillage would improve soil quality, and this might increase the potential for N supplying power of the soil and sustainability of crop productivity.     

Soil C balances in Swedish agricultural soils 1990–2004, with preliminary projections

Swedish agricultural land comprises about 3 Mha and its topsoil contains about 270 Mt C (0–25 cm depth). Based on daily climate data, annual yield data and a soil database, we calculate the topsoil C dynamics for Swedish agricultural land 1990–2004, using a soil C balance model, ICBM. Losses from high C (organic) soils are calculated from subsidence, which in turn is calculated from soil properties, cropping system and weather conditions. We also present scenarios and projections into the future. Mineral soils are close to balance in all of the eight agricultural regions investigated. Average soil C mass roughly increases from South to North, since the lower yields and thus C inputs in Northern regions are more than balanced by the higher decomposition rates due to warmer climate in the South. The higher proportion of grass leys in the North also contributes to higher C mass. High C soils (>7% C, corresponding to 12% soil organic matter content) lose 2–6 t C ha⁻¹ year⁻¹, depending on weather and cropping system, and total annual loss from Swedish agricultural high-C soils is about 1 Mt year⁻¹. This loss is discussed in the context of plant production and remedial actions. Projections into the future, assuming that a temperature increase leading to increased decomposition rates also will lead to higher yields, indicate a potential to at least maintain soil C mass in Swedish agricultural mineral soils. Growing crops with residues more resistant towards decomposition would be an efficient way to increase soil C mass. See also .     

Agro-ecological nitrogen management in soils vulnerable to nitrate leaching: a case study in the Lower Suwannee Watershed

Environmental benefits associated with reduced rates of nitrogen (N) application, while maintaining economically optimum yields have economic and social benefits. Although N is an indispensable plant nutrient, residual soil N could leach out to contaminate groundwater and surface water resources, particularly in sandy soils. A 2-year field study was conducted in an established bermudagrass (Cynodon dactylon) pasture in the Lower Suwannee Watershed, Florida, to evaluate N application rates on forage yield, forage quality, and nitrate (NO₃-N) leaching in rapidly permeable upland sandy soils. Four N application rates (30, 50, 70, and 90 kg N ha⁻¹ harvest⁻¹) corresponding to 0.33, 0.55, 0.77 and IX, respectively, of recommended N rate (90 kg N ha⁻¹ harvest⁻¹) for bermudagrass hay production in Florida were evaluated vis-à-vis an unfertilized (0 N) control. Suction cups were installed near the center of each plot at two depths (30 and 100 cm) to monitor NO₃-N leaching. The grass was harvested at 28 days intervals to determine dry matter yield, N uptake, and herbage nutritive value. Nitrogen application at the recommended rate produced the greatest total dry matter yield (~18.4 Mg ha⁻¹ year⁻¹), but a modeled economically optimum N rate of ~57 kg N ha⁻¹ harvest⁻¹ (~60% of the recommended N rate) projected an average dry matter yield of ~17.3 Mg ha⁻¹ year⁻¹, which represents >90% of the observed maximum yield. Nitrogen application increased nutritive quality of the grass, but increases in N application rate above 30 kg N ha⁻¹ did not result in significant increases in in vitro digestible organic matter concentration, and tissue crude protein was not significant above 50 kg N ha⁻¹. Across the sampling period, treatments with N rates ≤50 kg N ha⁻¹ harvest⁻¹ had leachate NO₃-N concentration below the maximum contaminant limit of <10 mg l⁻¹. Conversely, applying N at rates ≥70 kg N ha⁻¹ harvest⁻¹ resulted in leachate N concentration that exceeded the maximum contaminant limit, and suggest high risk of impacting groundwater quality, if such rates are applied to soils with coarse (sand) textures. The study demonstrates that recommendation of a single N application rate may not be appropriate under all agro-climatic conditions and, thus, a site-specific evaluation of best N management strategy is critical.     

Tillage and residue management effects on soil carbon and CO<Subscript>2</Subscript> emission in a wheat–corn double-cropping system

The mitigation of CO₂ emission into the atmosphere is important and any information on how to implement adjustments to agricultural practices and improve soil organic matter (SOM) stock would be helpful. We studied the effect of tillage and residue management on soil carbon sequestration and CO₂ emissions in loam soil cropped in a winter wheat–corn rotation in northern China. There were five treatments: mouldboard ploughing, rotary tillage and no-tillage with chopped residues (MC, RC and NC), additional no-tillage with whole residue (NW) and mouldboard ploughing without residue (CK). After 5 years of each tillage system, MC and RC had higher annual CO₂ efflux from soil. The CO₂ effluxes were correlated with the ratio of dissolved organic carbon to soil microbial biomass (DOC/MBC) among treatments. This effect may be due to less immobilization of soil carbon by microorganisms under long-time intensive tillage. Although both MBC and DOC showed seasonal variability, when averaged across the sampling period only MBC discriminated between treatments. After 5 years of tillage, all treatments except CK increased SOM (0.16–0.99 Mg C ha⁻¹ year⁻¹) at 0–30 cm depth and NC was the greatest, resulting from historical SOM depletion and large C return from recent residues. Despite the lowest CO₂ flux being from the NW treatment, lower input residue from decreased biomass may have lowered C sequestration. To improve soil C sequestration in rotations, the input of residue and the CO₂ emission should be balanced by adopting appropriate tillage and residue management.     

Relationship between residue quality,decomposition patterns,and soil organic matter accumulation in a tropical sandy soil after 13 years

The objectives of this study were to investigate decomposition patterns and soil organic matter (SOM) accumulation of incorporated residues (10 Mg ha⁻¹ year⁻¹) of different quality, and identify microbiological parameters sensitive to changes in SOM dynamics, in a 13-year-old field experiment on a sandy soil in Northeast Thailand. Mass loss was fastest in groundnut stover (high N), followed by rice straw (high cellulose) and tamarind (intermediate quality), and slowest in dipterocarp (high lignin and polyphenol) following a double exponential pattern. The decomposition rate k ₁ (fast pool) was positively correlated with cellulose (r = 0.70*) while k ₂ (slow pool) was negatively related to lignin (r = −0.85***) and polyphenol (r = −0.81**) contents of residues. Residue decomposition was sensitive to indigenous soil organic nitrogen (SON), particularly during later stages (R ² = 0.782**). Thirteen years’ addition of tamarind residues led to largest soil organic carbon (SOC) (8.41 Mg ha⁻¹) accumulation in topsoil (0–20 cm), while rice straw yielded only 5.54 Mg ha⁻¹ followed by the control (2.72 Mg ha⁻¹). The highest SON (0.78 Mg N ha⁻¹) was observed in the groundnut treatment. Increases in SOC were negatively correlated with cellulose content of residues (r = −0.92***) and microbial respiration (CO₂-C) losses, while SON was governed by organic N added. During later decomposition stages, there was a high efficiency of C utilization (low qCO₂) of decomposer communities especially under tamarind with the lowest qCO₂ and CO₂-C evolution loss. This study suggests that N-rich residues with low cellulose and moderate lignin and polyphenol contents are best suited to improve SOM content in tropical sandy soils.     

Increase of N2O Fluxes in Agricultural Peat and Sandy Soil under Elevated CO2 Concentration: Concomitant Changes in Soil Moisture, Groundwater Table and Biomass Production of Phleum pratense

The effects of elevated atmospheric CO₂ concentration on soil moisture, N₂O fluxes, and biomass production of Phleum pratense were studied in the laboratory. Farmed peat and sandy soil mesocosms sown with P. pratense were fertilized with a commercial fertilizer. In peat soil 10 g N m⁻² of commercial fertilizer were added and in sandy soil 15 g N m⁻². In both experiments, soil moisture was regulated with deionized water; 18 mesocosms were tended to keep equally moist, and the other 18 were watered with equal amounts of water. Nine mesocosms from both watering treatments were grown under ambient (360 μmol mol⁻¹) CO₂ concentration and the remaining nine under doubled (720 μmol mol⁻¹) CO₂. N₂O efflux was monitored using a closed chamber technique and a gas chromatograph. The elevated supply of CO₂ increased production of above- and belowground biomass, soil moisture and N₂O fluxes, but decreased the total N content in the aboveground biomass, especially for the sandy soil. In similar water levels, N₂O efflux from the sandy soil was the same magnitude as that from the peat soil. In addition to moisture, N availability was the main limiting factor for N₂O production, but C availability also seemed to regulate the denitrification activity. In addition to an increase in C availability the increase in the N₂O efflux under the raised CO₂ concentration also required a simultaneous increase in soil moisture.     

Effects of fertilization on nutrient budget and nitrogen use efficiency of farmland soil under different precipitations in Northeastern China

Based on a consecutive 16-year field trial and meteorological data, the effects of fertilization on the nutrient budget and nitrogen use efficiency in farmland soil under different precipitation years were studied. With no fertilization treatment, the grain yield of maize was 3,520 kg ha⁻¹ (mean yield over 13 years). But the maximum yield increased to 7,470 kg ha⁻¹ when treated with mineral N, P and K fertilizers and recycled manure. The nutrient uptake also increased by twofold to threefold in NPKM treated field compared with that in the control treatment. The highest yields were obtained in years with normal precipitation, despite the different fertilization schemes. The lowest yields were obtained in drought or waterlogging years, which were 44.7–58.5% of the yields in years with normal precipitation. It also appeared that the deficits of N, P and K were greater in the years with proper precipitation than those in arid or flood years, because more production was removed from the field. Soil total N decreased significantly when treated with mineral fertilizer or recycled manure alone. The maximum deficit of soil total N was observed in control treatment (557 kg ha⁻¹) from 1990 to 2005. The N treatment resulted in a significant negative balance of P, due to the high yield of the crop in response to applied N. The application of NP or N to soils resulted in a greater negative K balance than that of the control. The greatest negative balance of total P and available P were obtained under the control and N treatment, and the highest deficit of soil total K and exchangeable K were obtained under NP treatment. We found that the rate of 150 kg N ha⁻¹ year⁻¹ was inadequate for maintaining soil N balance, and amendment of soil with organic source could not stop the loss of soil P and K. The applying rates of 150 kg N ha⁻¹ year⁻¹, 25 kg P ha⁻¹ year⁻¹, and 60 kg K ha⁻¹ year⁻¹ combined with 2–3 t ha⁻¹ organic manure were recommended to maintain soil fertility level. The nitrogen use efficiency (NUE) was greatly improved in the years with proper precipitation and balanced fertilization. Higher NUE and grain yields were achieved under NPK and NPKM treatments in years with normal precipitation. The results clearly demonstrated that both organic and mineral fertilizers were needed to increase crop production, improve NUE and maintain soil fertility level.     

Grain legume rotation benefits to maize in the northern Guinea savanna of Nigeria: fixed-nitrogen versus other rotation effects

The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects, but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow. The plots were split into four N fertilizer rates (0, 30, 60 and 90 kg N ha⁻¹) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer rate. The legume genotypes fixed between 14 and 51 kg N ha⁻¹ of their total N and had an estimated net N balance ranging from −29.8 to 9.5 kg N ha⁻¹. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere. The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279 kg ha⁻¹ while rotation effects ranged between 193 and 513 kg ha⁻¹. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize, respectively.     

Effects of soil and crop management practices on yields,income and nutrients losses from upland farming systems in the Middle Mountains region of Nepal

On-farm runoff plots were established during 2004 and monitored for 4 years in the Pokhare Khola watershed (Nepal) in a completely randomized design with four replications of each three treatments: traditional Farmer Practice (FP) (Zea mays–Eleusine coracana), Reduced Tillage (RT; Z. mays–Vigna ungeuculata), and Commercial Vegetable with double dose of farm yard manure (CV; Z. mays–Capsicum species) to evaluate treatment effects on soil nutrient losses, nutrient balances and crop income on Bari land (rainfed terraces). Nutrient removal due to crop harvest was found to be significantly higher than nutrient loss through soil erosion, and CV treatment exhibited a significantly higher N uptake (123 kg ha⁻¹ year⁻¹) through crop harvest than other treatments. Moreover, the CV treatment produced significantly higher income per unit area of Bari land than the other treatments. Soil organic carbon and major nutrients losses (NPK) through soil erosion were minimal [25.5 kg ha⁻¹ year⁻¹ soil organic carbon (SOC) and 5.6:0.02:0.12 kg ha⁻¹ year⁻¹ nitrogen (N), phosphorus (P), potassium (K), respectively]. Result showed that no nutrients were lost through leaching. Nutrient losses due to soil erosion and runoff were lower than previously reported in the Middle Mountain region, indicating a need to re-evaluate the soil erosion and nutrient loss problems in this region. Interventions such as reduced tillage and double dose of FYM with vegetable production were found to be effective in maintaining soil fertility and increasing farm income compared to the traditional maize-millet production system. The nutrient balance calculations suggest that integrated nutrient management techniques such as residue incorporation and application of FYM with a minimum application of chemical fertilizer are potentially sustainable production approaches for the Mid-hills of Nepal.     

Nitrogen loss: an emerging issue for the ongoing evolution of New Zealand dairy farming systems

Here we present a case study of two New Zealand dairy farms located in the southern North Island (latitude 40°S) in which we review the evolution of the system over the past 30 years with particular focus on the relation between intensification and N loss to the environment. Over the period evaluated the two case farms lifted per cow production by over 40% and approximately doubled per ha milk production, partly through identification of efficiencies in farm system design and partly through intensification by feed importation. Based on the production data, animal consumption (t DM ha⁻¹ year⁻¹) and N loss to the environment (kg N ha⁻¹ year⁻¹) were modelled for four scenarios representing the two case farms in the early 1980s and in the 2007/2008 production season. For one case farm, the system was modelled for two further scenarios before and after changes aimed at increasing feed conversion efficiency. Increase in N loss to the environment from dairy farm operations arising from intensification between the early 1980s and the 2007/2008 season were largely offset by a change in the system of farm dairy effluent disposal that reduced N loss. Comparing model output for system configurations with low (38%) and high (49%) feed conversion efficiency, production was 893 and 1,115 kg milk solids (MS) ha⁻¹, N loss to the environment was 19 and 20 kg N ha⁻¹ year⁻¹, and ‘environmental efficiency’ was 21 and 18 kg N leached tonne⁻¹ MS produced, respectively.     

Carbon resources of residue and manure in Japanese farmland soils

This study calculated the carbon (C) input to farmland soils in Japan in an effort to investigate the potential increase in soil C of farmland soils by proper application of crop residues (straw and root) and manure. The calculation was based on inventory and activity data obtained from statistics, literature sources and inquiry reports for the year 2005. The total C resources from crop residues and manure in Japan were 6.1 Tg C year⁻¹ and 2.3 Tg C year⁻¹, of which 4.9 Tg C year⁻¹ and 1.9 Tg C year⁻¹, respectively, were applied to farmland soil. The average C application rate was 1.7 ± 1.6 Mg C ha farmland⁻¹ year⁻¹ and the proportion of manure was 23 ± 26%. One scenario that improved the allocation of manure and crop residue input to farmland soil increased the average C input to farmland soil to 1.8 ± 1.3 Mg C ha farmland⁻¹ year⁻¹. This agricultural C flow represented only a small percentage of the global warming potential of the whole of Japan. Thus, management of C resources in the agricultural sector should focus on the sustainable use of soil rather than the C sequestration potential of soil. To improve the C flow for areas with high C input, the transportation of manure to neighboring municipalities failed to reduce the excessive amount of manure since those areas are concentrated in only a few regions. Other measures were required to reduce environmental problems due to the over-supply of manure to farmland soils. For areas with low C input, the introduction of green manure, changes in cultivation methods, and land use type itself must be considered in relation to the individual C requirements specific to land use, soil type and climate conditions.     

Benefits of integrated soil fertility and water management in semi-arid West Africa: an example study in Burkina Faso

The synergistic effect of soil and water conservation (SWC) measures (stone rows or grass strips) and nutrient inputs (organic or mineral nutrient sources) was studied at Saria station, Burkina Faso. The reduction in runoff was 59% in plots with barriers alone, but reached 67% in plots with barriers + mineral N and 84% in plots with barriers + organic N, as compared with the control plots. Plots with no SWC measure lost huge amounts of soil (3 t ha⁻¹) and nutrients. Annual losses from eroded sediments and runoff reached 84 kg OC ha⁻¹, 16.5 kg N ha⁻¹, 2 kg P ha⁻¹, and 1.5 kg K ha⁻¹ in the control plots. The application of compost led to the reduction of total soil loss by 52% in plots without barriers and 79% in plots with stone rows as compared to the losses in control plots. SWC measures without N input did not significantly increase sorghum yield. Application of compost or manure in combination with SWC measures increased sorghum grain yield by about 142% compared to a 65% increase due to mineral fertilizers. Yields increase did not cover annual costs of single SWC measures while application of single compost or urea was cost effective. The combination of SWC measures with application of compost resulted in financial gains of 145,000 to 180,000 FCFA ha⁻¹ year⁻¹ under adequate rainfall condition. Without nutrient inputs, SWC measures hardly affected sorghum yields, and without SWC, fertilizer inputs also had little effect. However, combining SWC and nutrient management caused an increase in sorghum yield.